The present invention relates to a magnetic head, and particularly to a tunnel erase type magnetic head which has a recording and reproducing head core and an erasing head core, and which can be suitably adapted to a floppy disk apparatus for high-density magnetic recording.
A magnetic head widely used in the general floppy disk-type magnetic recording and reproducing apparatus has been disclosed in Japanese Patent Laid-Open No. 44219/1982, having a structure as shown in FIG. 10.
That is, as shown in a plan view of FIG. 10 which views the magnetic head from over a surface facing the recording medium, the above-mentioned conventional magnetic head consists of a magnetic recording and reproducing head 10 composed of ferrite, an erasing head 11 and a nonmagnetic material 12 which blocks the magnetic effect between the two heads.
Unlike a rigid disk apparatus, the floppy disk apparatus requires interchangeability of disk. That is, it is required to provide an erase band between the tracks on which signals are recorded, in order to maintain interchangeability among the apparatuses and magnetic recording media, and to correct the shift of rotary shaft of a drive device or the shift of recording medium chuck and to correct the expansion or contraction of the medium and mechanical parts caused by the change of temperature and humidity. In a floppy disk without a track servo mechanism, it is necessary to prevent the effect from the neighboring tracks.
For this purpose, a tunnel erasing method is employed in which an erasing head core 11 is arranged at the back of the recording and reproducing head core 10 as shown in FIG. 10 in order to trim both edges of the track on which the signals are recorded. In this tunnel erasing system, there is arranged the nonmagnetic material 12 to prevent magnetic effect between the two heads.
Operation of the magnetic head will now be described in conjunction with FIG. 11. First, a signal is recorded onto a region 15 of a track width l.sub.1 of a magnetic gap 13 of the magnetic recording and reproducing head 10, and then overlapped portions d.sub.1, d.sub.2 are erased as erasing regions 16 by a magnetic gap of the erasing head 11, whereby the practical width of the recording track becomes as denoted by l.sub.2. The overlapped portions d.sub.1 and d.sub.2 remain constant in the apparatus in which the recording medium moves linearly. In an apparatus which undergoes a circular motion such as a floppy disk, however, the overlapped portions d.sub.1 and d.sub.2 vary depending upon the radial direction r of the medium and a distance L between the magnetic gap 13 for recording and reproducing the signals and the magnetic gap 14 for erasing the signals.
This relationship will now be described with reference to FIGS. 12 and 13. FIG. 12 shows the case where the distance L is small and FIG. 13 shows the case where the distance L is large. As the distance L increases as shown in FIG. 13, the effective track width l.sub.2 ' after erasing becomes smaller than the distance l.sub.2 between the erasing gaps. Therefore, the effective track width decreases in larger amounts on the inner side of the medium than on the outer side, and this tendency becomes conspicuous as the distance L increases. Further, the overlapped portions d.sub.1 and d.sub.2 assume different widths, and the under-erasing and over-erasing take place. Because of this fact, the distance L must be reduced between the magnetic gap 13 for recording and reproducing the signals and the magnetic gap 14 for erasing the signals as shown in FIG. 12.
When the apparatus has a high track density or when the floppy disk has a small medium diameter, in particular, the distance L plays an important role.
If thickness of the nonmagnetic material 12 is reduced or if the nonmagnetic material 12 is not provided to solve the above-mentioned problem, the magnetic flux of the recording and reproducing head is affected by the magnetic flux of the erasing head, and recording error takes place. If thicknesses of the two head cores are reduced, on the other hand, the magnetic path loses the efficiency and the mechanical strength is lost.
In the conventional head, furthermore, the core is composed of a ferrite, and the signals are not sufficiently recorded onto a medium having a high coercive force such as a metal floppy disk; i.e., the head is not adapted to the high-density recording apparatus. In order to solve such a problem, European Patent Laid-Open No. 0140977 discloses a tunnel erasing-type magnetic head in which a portion constituting a magnetic gap surface of the magnetic head is coated with a magnetic layer of a high saturation flux density. As a prior application of such a magnetic head, furthermore, there can be cited U.S. patent application Ser. No. 739,447 (which is simply a prior application but is not a prior art). By using the thus constructed tunnel erasing-type magnetic head, the signals can be sufficiently recorded even onto a medium having a high coercive force, accompanied, however, by such defects as reduced effective track width and the development of under-erasing and over-erasing.
The following references are cited to show the state of the art; Japanese Patent Laid-Open Nos. 185015/1984 and 256904/1985.